The presence of liquid water in fuel cells is unavoidable because of water generated during fuel cell operation. In addition, water is brought into the fuel cell by humidified gases. Water is needed for proper humidification of the proton exchange membrane. At the same time, excessive water accumulation in the flow field channels on either anode or cathode sides of the fuel cell can cause numerous problems including reduced fuel cell performance and reliability due to uneven reactant distribution and local reactant starvation in the fuel cell; increased gas flow resistance in some channels diverting the flow to other channels (within cell flow sharing); increased gas flow resistance of particular cells in the stack diverting the flow to other cells (cell to cell flow sharing); increased overall fuel cell stack flow resistance exerting parasitic load on the system components, such as air blower/compressor; and reduced reactants efficiency and economy. These phenomena dictate the need for improved water management.
Increased wettability (hydrophilicity) of the flow field channels helps to spread water droplets and thus prevents channel blockage, and promotes water removal via the film flow along the channel walls and via capillary mechanisms. Flow field channels with extremely hydrophobic surfaces may require less time to remove water because water droplets are very unstable on such surfaces. What is needed is improved water management in the fuel cell.
Moreover, the surface electrical conductivity significantly contributes to the total intrinsic electrical conductivity of carbon-based materials. Thus, improvement of the surface electrical conductivity of composite and graphite separator plates could increase the overall fuel cell stack electrical conductivity.